Project Summary We propose a collaborative project involving immunologists experienced in autoimmune diabetes, mass-spectrometrists, and endocrinologists-diabetologists. Our combined efforts are to specifically identify relevant peptides from beta cell proteins involved in the immunopathogenesis of type 1 diabetes. The project combines experimental studies in diabetes-prone mice that should lead to targeted evaluation of human samples. The ultimate goal is to identify peptides that form the substrate for the autoreactive MHC-II response that initiates and perpetuates the process. Important is to identify relevant diabetogenic antigens at different stages of the autoimmune reaction from pre-diabetes to the initial progression: it will include their characterization, source in beta cells, involvement in the disease process, and sites of presentation. Aim 1 consists of an identification of novel peptides derived from beta cell granules of both mice and humans. We examine vesicles isolated from beta cells with a major focus on crinosomes. Crinosomes and insulin dense core granules will be isolated during different stages of diabetes development, their peptides will be isolated and examined by sophisticated mass spectrometry with state of the art instrumentation and technology. We will place emphasis in unique structural or post translational changes in peptides and whether the panoply of them changes as the beta cell progresses into active diabetes. We also will examine vesicles and exocytosed products from human islets from recently diseased individuals. Aim 2 will be an immunological validation of novel peptides identified by mass spectrometry. Immunological and biochemical assays will be used to validate the ability of beta cell derived peptides to bind to I-Ag7 and activate T cells in vitro and in vivo. Aim 3 will be the Identification and validation of the MHC-II-bound peptidome in islets and secondary lymphoid organs. We plan to examine the peptidome eluted from MHC-II molecules expressed by phagocytes obtained from islets, peripheral lymph nodes, and spleens of the NOD mouse and to characterize/validate them as in Aims 1/2. This is the seminal test to prove an immunogenic peptide, that is, it's a positive identification bound in vivo to MHC-II alleles.